Force RDF data to be UTF-8
The RDF reader chokes on certain character combinations if the raw data
is not encoded UTF-8.  See https://github.com/ruby-rdf/rdf/issues/142
Fedora does not store character encoding, so by default they come back as
ASCII-8BIT.
Merge pull request #287 from projecthydra/rdf_encoding_6.7

Force RDF data to be UTF-8